1. Field of the Invention
The present invention is directed toward beltless conveyors and, more specifically, to a shaker conveyor having an electronically controllable stroke speed.
2. Description of the Related Art
Conveyors are well known material handling devices that have application in a wide variety of environments for transporting objects from one place to another. For example, one type of conveyor employs a belt formed into an endless loop which is entrained about at least a pair of rollers spaced apart from one another and usually located at the opposed marginal ends of the conveyor. The rollers have sprockets at either end thereof. The spaced rollers are interconnected by a pair of chains entrained about the sprockets at either end of the rollers. An electric or hydraulic motor is usually employed to power the sprockets and continuously moves the belt over a substantial length of the conveyor between the rollers. In this way, objects may be transported by the conveyor over its length.
Conveyors often find applications in manufacturing environments. For example, in metal stamping operations, conveyors are employed to move parts between successive presses or from a press into a bin. In addition, conveyors are used for inspecting, transporting and assembly situations and can assist in maximizing production by removing parts, slugs or other scrap and materials from under low clearance areas like punch press dies and permitting continuous operation of the press. However, belted conveyors suffer from the disadvantage that the belts are often cut by the sharp edges of the metal parts formed in stamping operations. The useful life of the belts are reduced and the belts must be replaced more frequently. Frequent belt replacement increases the maintenance costs of the stamping operation. Further, stamped parts and other debris may pass through the damaged belts and jam or foul the inner workings of the conveyor drive system.
In part to avoid these problems, beltless conveyors are often employed in certain manufacturing operations. One type of beltless conveyor known in the related art moves items along the length of a conveyor by a physical reciprocating action. The material to be moved is transported in or on a table, channel, or trough. The reciprocating action of the conveyor is faster in one lineal direction than the other thereby causing the material to be moved with each forward stroke of the conveyor. The inherent reciprocating action of these types of beltless conveyers causes them to be generally referred to as shaker conveyors. Shaker conveyors obviously do not suffer from cuts or worn belts and thus have been adopted in numerous manufacturing environments.
A shaker conveyor may even be used to transfer corrosive, high-temperature, heavy, or other difficult to transport materials from place to place. For example, hot metal castings, particulate material, or other material difficult to transport due to physical or chemical characteristics can be transported by a shaker conveyor. The flexibility as to different types of materials is derived from the conveyor table or trough, which supports the material being carried. The shaker table can be made of materials resistant to heat, corrosion, or physical or chemical problems caused by the items being conveyed.
As previously mentioned, to convey the items or material on the table, the shaker table is accelerated in the direction of a desired material movement to reach a maximum forward velocity and then the direction of movement of the table is rapidly reversed so that the material slides along the table in the desired direction. As the table moves in the reverse direction, the material decelerates and comes to rest, and is then subject to the next reciprocal forward movement of the table so that there is little or no backward sliding of material being conveyed. In this manner, during one of the reciprocal movements, or strokes, the table provides a griping action on the material being conveyed. Conversely, the table provides a sliding action on the material being conveyed during the opposite reciprocal movement.
There are a number of conventional prior art shaker mechanisms that achieve the desired result of a forward motion of material by using a reciprocating action. These conventional shaker conveyors use crankshafts or other eccentrics with linkage arms to achieve the desired reciprocal motion, often with heavy flywheels. The linkage arms are pivotably attached to the flywheel or eccentric at one end and are likewise pivotably attached to the shaker table at the one ends. By the inherent physical differences designed into the linkage arms or the placement of their attachment points, or through the use of a cam or other physical device, the reverse movement of the shaker table may be faster than the forward movement. While these types of drive mechanisms provide satisfactory reciprocal motion, the operating elements and linkages are complex, and tend to be difficult to manufacture. These complex shaker assemblies are also expensive to maintain. More specifically, the linkage arms used to provide the reciprocating motion have a tendency to get out of line, reducing the efficiency of the shaker and causing further operational problems.
Furthermore, having a number of linkage arms with generally fixed attachment points, or the use of a cam or other physical device to establish the speed of the forward and reverse strokes of the shaker table makes speed adjustments to the shaker table problematic. Efficient shaker conveyance of materials directly relates to tailoring the proper forward and reverse strokes speeds of the shaker for the particular material or items being conveyed. In conventional shaker conveyors, the tailoring, or tuning of the shaker stroke speed is accomplished by the design of the linkages, or more specifically, by the length of the linkage arms or the placement of their associated attachment (fulcrum) points. If a cam or other physical device establishes stroke speed, then tuning the stroke speed relates to the shape or profile of the cam assembly. However, the tuned efficiency of the prior art conveyors for conveying heavy material loads does not directly translate to conveying lighter loads, nor does the tuned efficiency of conveying light loads translate to conveying heavy loads. More specifically, with conventional shaker conveyers, when it is desired to change the speed of the strokes that are tuned for conveying one type of item of a particular weight to convey another item of different weight, the linkage arms must be replaced or their linkage points must be physically relocated to tune the stroke speed of the shaker to the new material. If a cam or other physical device establishes stroke speed, then the cam must be changed to alter the stroke speed. Therefore, not only is the initial tuning of stroke speed for conveying a particular material time consuming and inefficient, but any adjustments to the stroke speed of the shaker for the conveyance of different materials is inefficient, time-consuming, and difficult to perform. Likewise, if during the course of operation, it becomes apparent that the conventional shaker table has lost conveying efficiency due to wear or slight changes in the conveyed material, it is nearly impossible to adjust the stroke speed of the conveyor to overcome the loss of efficiency without major, time-consuming changes to the linkages.
Thus, there exists a need in the art for a shaker conveyor assembly that is of simple and efficient construction and that has an adjustable stroke speed. In addition, there remains a need in the art for a shaker conveyor assembly that is electronically controllable.